Artificial line



4 AAAAAAAL VVVaVVVV Sept. 28, 1926. 1,601,037

I H. NYQUIST ARTIFICIAL LINE Filed Sept. 2, 1921 INVENTOR ATTORNEYPatented Sept. 28, 15926.

UNITED STATES PATENT OFFICE.-

HARRY NYQUIST, OF ELMHURST, NEW YORK, ASSIGNOR T AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

ARTIFICIAL LINE.

Application filed. September 2, 1921. Serial No. 497,843.

This invention relates to an artificial line for duplex telegraphy andhas for one of its objects that of producing an artificial linewhichconsists principally of fixed elements having preassigned values sothat a balance may be obtained by the adjustment of a minimum number ofelements. A second object is to produce an artificial line which willmake possible the maintenance of the balance for the system, althoughthe line itself may undergo various physical changes, such astemperature changes. Still another purpose is to make such an artificialline which can be readily adjusted for temperature or other changeseither by a simple and convenient hand adjustment, or by automaticadjustment brought into operation by the changes to be compensated.

Artificial lines for duplex telegraph lines have been used heretoforeand arrangements provided to permit adjustments for temperature or otherchanges taking place over a long length of line, but it has beennecessary to include in the artificial line variable capacities andresistances, practically all of which had in general to be adjusted in Iorder to bring about suitable balance. In

my invention it is the purpose to obtain this adjustment or compensationby varying resistances only and preferably by varying a minimum numberof. the resistances involved.

In the case of telegraphy over a pair of wires included in a cable, theonly climatic elements which need be considered as afiecting the lineare temperature changes. These in general produce no substantial effectupon the shunt capacity and leakage of the pair,

but do have an important and appreciable efl'ect on the resistances ofthe pair of conductors themselves, this change being sufiicient tovitiate the balance at a given temperature afiorded by the artificialline, and it is this change which makes it necessary to adjust from timeto time the constants of the artificial line. Since in such a pair ofwires the only change which need be considered is that due to the changeof resist-.

ance of the conductors, it seems that it should be possible with anartificial cable of the proper characteristics to make the necessarycorrections on compensations by changes in the series resistance of theartificial line only,

and in accordance with my invention it is proposed to use such anartificial line.

The invention will be better understood by reference to the followingspecification and the accompanying drawing, in which Figure l'representsa transmission line made up of an infinitely large number of sectionscontaining resistance R and inductance L in series in the line, andcapacity C and conductance G in shunt across the line. In case the lineis non-loaded the inductance L becomes substantially equal to zero, andin case the line is loaded the line may be considered as made up ofsections of appreciable size, in which R, L, C and G are the constantsfor a length of line corresponding to each loading section.

Fig. 2 represents a form of artificial line,

the characteristics of which will be develr oped later, and consistingof a large number of sections of the form shown.

F igs. 3 to 5 represent general forms of artificial lines which embodythe characteristics of my invention. Fig. 6 represents a telegraphtransmission line with which is associated my artificial line and alsothe telegraph apparatus which is intended for duplex operation on theline, and Fig. 7 shows in detail the mechanical arrangements forautomatically compensating for temperature or other physical changes inthe The invention will be made more clear byan analytical considerationof the properties ofthe lines of Figs. 1 and 2; The characteristicimpedance of the line of Fig. 1 is G+ipC and its propagation constant iswhere p nals 27! times the wave frequency and 'i'.= 1.

Similarly the impedance over the line of Fig. 2 would be R1. Z: G+ipC1+NG+@C) in which the quantity under the numerator R represents theconductance per section across the line. It can readily be shown thatthis impedance will be equal to the impedance of the The propagationconstant however will be different and'will be given by RO-GL mam Theartificial line then would take on the form shown in Fig. 3, in whicha:b:d=R,

and in which it being understood that for an infinitely long telegraphline there should be an 1nfinite number ofsections in the artificialline.

It is seen from this that C is a condenser which has a capacity equal tothe shunt capacity of any desired section of the trans mission line anda has the resistance of the same section of line, while 9 r) isproportional to the inductance of the same section of line. In case theline is non-loaded, the inductance is substantially equal to zero andtherefore r equals zero.

However, the expression for the impedance iven above was obtained on theassumption of a line of infinite length and infinitely small sections.If the sections are not Very short, the above expression is approximateonly and the exact formula is:

If each section of the network is made to correspond to n sections ofthe line, the impedance of the network then becomes:

and to a first approximation this becomes: Z=z P g+ P The ex ression inthe brackets may be considere as a correction factor due to the factthat the sections are not infinitely short, and the correction varies asthe square of n. For close simulation, therefore, it is desirable tomake 71. small but in order to simplify the apparatus it is desirable tokeep the number of sections of the artificial network small, which meansa corresponding increase in n. In practice I find that if the line doesnot exceed one or two hundred miles a sufiiciently close simulation ofthe actual line may be obtained with a network of three sections, asshown in Fig. 3.

I have discovered, and it is a part of my invention,'that the departureof the circuit of Fig. 3 from correct simulation, as 'ven in equation 1,can be almost compfie tely taken care of by inserting a resistance 6 ofthe proper size ahead of the first section of the network and this canin general be done 1; bringing a part of the resistance of the e ement ain front of the first condenser so that the artificial network takes onthe form of Fig. 4. The simulations may be further improved by changingthe value of f to f this change being, in general, an increase. Therelation e+a=b would naturally hold, in general, but I find that this isnot essential. It still remains true, however, that the sum of theseries resistance 6, a, b and (Z, should equal the series resistance ofthe line, which it is to balance. The particular value to be given to eand f can be determined by experiment for any given circuit, variousvalues being introduced until the amount of the unbalance is reduced toa minimum. Having once. obtained this for a given circuit however, thereis no need for further change.

Fig. 5 shows an artificial line similar to that of Fig. 4 but designedto balance a cable or line having no inductance. Accordingly theresistance elements such as g and h are omitted from the shuntconnections of the network. A resistance f will, however, be retained inthe shunt connection including the capacity Although its value will edto balance the inductance of a section of the line. As stated inconnection with Fig. 4, the resistances e and f are adjusted empiricallyafter the, remainder of the network las been computed, the empirical adustment being necessary to compensate for factors disregarded in thecomputations, which assume practically perfect conditions.

Thus far no consideration has been given to the terminal apparatus atthe' far -end of the telegraph line. Such apparatus, however, will havean influence, which should be accounted for in the balancing network,and I find that this can be done by an alteration in the resistance (1of the last section of the network, (see Fi "s. 3, 4 and 5), that beingthe proper place or such correction since the last section and theterminal apparatus are both furthest removed from the point ofconnection of the line and the network. For this reason d will ingeneral be made somewhat larger than I).

In view of the above it is seen that the characteristic equations for mynew network are as follows:

where c is the capacity per section of the line to be balanced, L and Rare the inductance and resistance for n sections of the line and e, r,and T are determined experlmentally for any given line and termlnalapparatus.

As mentioned earlier in the specification, telegraph lines of the typeunder conslderation, are subject to climatic-variations and, inparticular, to change in temperature. In the case of a pair of wires,-included in a cable, the only change which is of any importance is thechange in the resistance of the line. This change is of suflicientmagnitude to seriously upset the balance for duplex work and as a partof my invention I prbvide an arrangement of elements which will permitof a ready alteratlon of the necessary elements in order that thetemperature changes may be compensated. I find that suitablecompensation can be secured by changes in the series resistance of mybalancing network making it unnecessary to supply condensers of variablecapacity. To this end I make each of the resistances a, b

and d, adjustable, this being better illus- 14. These contacts arecontrolled by relay 16, the winding of which includes the groundedbattery 17 and the grounded key 18. As shown in the circuit, when thekey 18 is depressed, the relay 16 is operated to connect positiveofbattery 12 on one side of the line and negative to the other side.Upon opening the key 18 the contacts are released and reverse theconnection of the battery 12 to line. A filter to eliminate highfrequency impulses may be inserted between the transmitter and the line,this filter comprising inductances 20 and 21 in series with the batteryand condenser 22 in shunt. On the s de of the relay coils remote fromthe line is connected my balancing network N and when the line isproperly balanced the current from the battery 12 divides equally, halfof the current flowing to the line and half to the network. Under theseconditions the vibrating member of the relay 11 shown at 14 will not beaffected by such transmitted impulses, but impulses coming from theremote station will be effective to operate the vibrating member, which,in turn, may be used to control a sounder 24 associated with a battery26 in a manner well known in the art.

While the resistance a, b and'd may be made variable in any desired way,the figure 6 shows the variable Portions a 12,, and d connected on theother side of the line from fixed portions 11, b and d. Also thevariations (1, b and (i, may be made se arately, although for the sakeof simplicity in operation I find it desirable to vary thesesimultaneously and in the same direction. These variable resistancesmay, for example, be dial resistances, the dials being mounted one abovethe other and havin a common shaft carrying contacts over eac of thevariable resistances. Under these circumstances the operator may adjustthe network from time to time as it is found necessary in order tomaintain suitable balance of the line.

The networks illustrated in Figs. 3, 4 and 5 will be seen to possess anumber of i1nportant advantages, whereas, with networks of the priorart, made up of combinations of series of resistances and shuntconnections including capacities and resistances, all of the elementswere made adjustable, and each element was adjusted separately by anempirical method until a balance was attained. The adjustment of thevarious elements of such a network is purely a matter of cut and try andhas no necessary relation-to the theoretical requirements for balance.In accordance with the present invention, the series elements a, b and dare computed in advance, and the same holds true for the built up withthese elements fixed is then connected in a balancing circuit forbalancing a line of the type for which it is designed, and the elementseand f (which are adjustable) are then adjusted empirically until thebest. balance is obtained. Each time the element 8 is increased, theelement a will be decreased, or vice versa. When the proper balancehasbeen obtained, the elements e and f may be fixed, and the artificialline may be sent out to the field for use in the plant. The automatic adustment of the elements a, b and d is a simultaneous adjustment merelyintended to take care of variations in the resistance of the line to bebalanced and has nothing to do with the design of these elements at thefactory, the latter design being made with reference to a line which isassumed to have fixed characteristics.

The variation of the series resistances may be controlled automaticallyand in Fig. 7 w

I show one type of mechanism adapted for such automatic control,although it is apparent that a large variety of expedients might be usedfor this purpose. In this Fig. 7 is shown a Wheatstone brid e containingtwo fixed arms R and R third arm consists of a fixed resistance R inseries with a variableportion of a resistance R The fourth arm of thebridge consists of the remainder of the resistance R and a resistanceR,, which latter ma be a resistance subject to substantially e sametemperature as the cable conductor to be balanced or it may be a pair ofwires included in the same cable as the line to be balanced. In general,I find that for telegraph lines which do not exceed one or two hundredmiles in length, the temperature change is sufliciently uniformthroughout this whole line so that the changes are sufiicientlyproximatcd by a concentrated resistance at the transmitting station,this resistance being preferably exposed to the external temperaturechanges. The bridge is supplied with battery 8 and an indicator relay 3which relay is connected to the resistance R at an adjustable point bythe contact arm 8,. The contact arm S, is mounted on a shaft S whichshaft also carries the contact arms for the variable resistances 11,, b,and d The'arm S may be operated in one direction or another by the tworatchets 31 and 32, these ratchets, in turn, being operated by levers 33and 34. In proximity to these levers are arranged the magnet coils 4,,5, 6 and 7. The relay 3 controls a circuit including bpttery 9, relaylO and the magnet coils 4 to a The operation of the bridge is asfollows: In case the resistance R, increases the balance of the bridgewill be destroyed. Current will then flow through the relay 3 in such adirection as to operate its contact to close circuit 9, 10, 4 and 7. Theoperation of the magnet 7 will lift the lever 34 away from the ratchet32 and at the same time the operation of the magnet 4 will cause thelever 33 to advance the ratchet 31. The relay 10 will intermittentlyopen this circuit, causing a continuous step by step 0 eration of theratchet 31 and a correspon 'ng advancement of the contact S untilbalance of the bridge is restored. Corresponding changes will thus bemade in the resistances a 1),, and al In case the resistance R, falls,the contact of the relay 3 will then close circuit through battery 9,rela l0 and magnet coils 5 and 6, which wil cause a correspondingoperation of the arm S, in the reverse direction, and a corres ondingchange in the resistances a,, b, and

Although I have described an automatic arrangement of one form, it isapparent that numerous changes may be made in this mechanism as well asin other parts of the disclosure, without departing from my invention.

What is claimed is:-

1. A balancing network for a telegraph circuit comprising a plurality ofsections, each having a resistance in' series and a series combinationof resistance and capacity in shunt, a portion of the series resistanceof the first section being placed in front of the capacity of saidsection to correct for limited number of sections.

2. A balancing network .for 'a telegraph circuit comprising a pluralityof sections each having a resistance in series and a series combinationof resistance and capacity in shunt, a portion of the series resistanceof the first section being placed in front of the capacity of saidsectlon to correct fora limited number of sections, the shunt resistanceof the first section differing from the shunt resistances of othersections by an amount determined by the series resistance of thatsection.

3. A balancing network for a telegraph circuit comprising a plurality ofsections each having a resistance in series and a series combination ofresistance and capacity in shunt, a portion of the series resistance ofthe first section being placed in front of the capacity of said sectionto correct for a limited number of sections, the shunt resistance of thefirst section differing from the shunt resistances of other sections byan amount determined by the series resistance of that section, and thevalues of the series-resistance in front of the capacity of the firstsection and the shunt resistance of the first section being determinedby the constants of the circuit to be balanced.

4. A balancing network for a telegraph circuit comprising a plurality ofsections, each having a resistance in series and a series combination ofa fixed resistance and fixed capacity in shunt, the series resistance ofthe last section being in part determined by the resistance of theremote terminal apparatus, the total series resistance of the sectionsexclusive of the part of the last section determined by the terminalequipment being equal to the series resistance of the line.

5. A transmission line, a balancing network therefor containing capacityand resistance impedances forming series and shunt elements, all of saidelements except series resistances being fixed, said series reistancesbeing adjustable in proportion to temperature variations of the line toeffect a balance.

6. A transmission line, a balancing network therefor containing shuntcapacity and series resistance elements and adapted to be adjusted inaccordance with climatic variations of the line, said adjustment beingeftected by variations of the series resistance elements only inproportion to said climatic variations, the shunt capacity elementsbeing fixed.

7. A balancing network for a telegraph line comprising a plurality ofsections, each having a resistance in series and a capacity in shunt,and means operating in response to physical variations in the line tovary said network in accordance With said physical variations. Y

8. In combination, a balancing network for a transmission line, andmeans operating in response to physical variations in the line to varysaid network automatically in accordance with said physical variations.

9. A balancing network for a telegraph circuit comprising a pluralityof. sections, each having a resistance in series and a series resistanceand capacity in shunt,"and temperature controlled means for varying saidnetwork automatically in accordance with temperature variations.

10. A balancing network for a telegraph circuit comprising a pluralityof sections, each having a resistance in series and a se-- riescombination of resistance and capacity in shunt, and temperaturecontrolled means for varying the resistance. of the elements in saidnetwork in accordance with temperature variations in the line.

11. A balancing network for a telegraph line comprising a plurality ofsections, each having a resistance in series and a series combination ofa fixed resistance and fixed capacity in shunt, and means for varyingthe series resistance of said network in proportion to temperaturevariations in the line.

12. A balancing network for a telegraph sections, each having aresistance in series and a series combination of resistance and capacityin shunt, certain of said elements being variable and a lVheatstonebridge, one arm containing an elementsubject to line variations andmeans controlled by said bridge to vary the variable elements of saidnetwork in accordance with the line variations.

14:. A balancing network for a telegraph line comprising capacities andresistances, and means for simultaneously adjusting a plurality of saidresistances in proportion to and in response to climatic variations inthe line.

15. A balancing network for a telegraph linecomprising capacities andresistances, and means for simultaneously and automatically adjusting aplurality of said resistances in accordance with and in response toclimatic variations in the line.

16. A balancing network for a telegraph circuit comprising seriesresistance and fixed shunt capacity and fixed shunt resistance, and meanfor simultaneously adjusting a plurality of said series resistancesm proportion to and in response to climatic variations in the line.

In testimony whereof, I have slgned my name to this specification this29th day of August 1921.

HARRY N YQUIST.

